The present invention relates to the generation of one or more sinusoidal waveforms representative of variables and, more particularly, to the generation of one or more 3-level waveforms which approximate sinusoidal waveforms representative of a variable. It more specifically relates to the generation of two 3-level waveforms approximating the sine and cosine values of an angular variable.
Many resolver transducers and the like now available for sensing the value of an angular variable are excited by analog signals formed by linear circuitry. In some instances it has been necessary to include a "digital-to-resolver converter" to provide the desired analog signals. These converters have circuitry similar to digital-to-analog converters, except that trigonometric sine and cosine relationships must be somehow calculated, such as with a look-up table or a specially constructed analog network. Some resolver transducers also are designed to rely on the combination with the outputs of the resolver stators, of analog signals representative of the sine and cosine of an angular input variable to enable the angular position of the resolver rotor to be determined. In other words, the provision of analog signals by linear (active) circuitry has been a significant requirement of resolver transducers. It is desirable, however, to minimize the use of linear circuitry in satellite, space station or robotic structures that must perform long-lived missions in a hostile space environment. Analog components are subject to drift problems and their stability is quite sensitive to the radiation exposure that is found in space.